1. Field of the Invention
The present invention relates to a method for forming quantum dots, and more particularly, to a method for forming quantum dots usable as an active layer of a photonic device such as a laser diode or a photodetector.
2. Description of the Related Art
There have been variously studied on a Stranski-Krastanow growth method for growing self-assembled quantum dots using a strain relaxation process of a lattice-mismatch without an additional lithography process. In addition, there have been made various studies on applications of the self-assembled quantum dots formed by the Stranski-Krastanow growth method to photonic devices.
In particular, studies on applications of the self assembled quantum dots in optical communications using a wavelength between 1.3 μm and 1.55 μm have been briskly made. In(Ga)As quantum dots may be taken as an example of quantum dots used in a wavelength of 1.3 μm. The In(Ga)As quantum dots may be grown from a GaAs substrate using a self assembled method. Thus, many results of studies on laser diodes and photonic devices using the In(Ga)As quantum dots formed by the self-assembled method as active layers have been announced.
However, in a case where In(Ga)As quantum dots are formed on a GaAs substrate so as to be used in a wavelength of 1.55 μm, there is a limit to realizing the wavelength of 1.55 μm due to sizes of the In(Ga)As quantum dots and effects of strains of peripheral materials. Thus, active studies on forming of In(Ga)As quantum dots used in a wavelength of 1.55 μm on an InP substrate have been made.
However, in a case where the InP substrate is used, a lattice mismatch between the InP substrate and a material for forming quantum dots is lower than when a GaAs substrate is used. Also, it is highly difficult to form high-quality quantum dots using a self-assembled method due to a reaction of the InP substrate with peripheral materials. Moreover, In(Ga)As quantum dots formed on the InP substrate are asymmetric or non-uniform. Thus, a full-width at half-maximum (FWHM) of a photoluminescence peak is highly wide, and an intensity of the photoluminescence peak is weak. As a result, many problems occur in the use of the In(Ga)As quantum dots as an active layer of a photonic device.